Twinkle, Twinkle, Christmas Star, How I Wonder What You Are!


By Knicole Colon, PhD

While not all people celebrate Christmas, it is commonly known that in the Christian religion, the “Christmas Star” or the “Star of Bethlehem” is what led the wise men to find the newborn baby Jesus in Bethlehem. The story goes that the wise men saw the Christmas Star and believed it signified the birth of the King of the Jews. They traveled to Jerusalem to ask King Herod where they might find such a child, and the king’s advisors informed him that Bethlehem was the likely birthplace of the baby Jesus. So, the wise men traveled to Bethlehem, and indeed found the baby Jesus there. It is said in the Gospel of Matthew that “the star which [the wise men] had seen in the East went before them, till it came and stood over where the young Child was.” The wise men were overjoyed to find that the star marked the location of the baby Jesus because it meant they had indeed found the Messiah.

I find this story interesting because, as an astronomer, I cannot help but wonder if the Christmas Star was a real astronomical object. I am not the first to wonder this by any means. In the early 1600s, the astronomer Johannes Kepler calculated that a conjunction of Jupiter and Saturn occurred in the year of Jesus’ birth. Such a conjunction (i.e. that the planets appear to be close in the sky) could have made the two planets appear as one bright object in the sky. However, recent calculations suggest that Jupiter and Saturn were far enough apart that they would not have appeared as an exceptionally bright single object. However, conjunctions between Venus (the brightest planet in the sky) and Jupiter might have instead been the source of the Christmas Star. The astronomical timeline of the conjunctions of these two planets fits the story pretty well, though there is still some controversy since these planets (which would appear as a single planet in the sky at this time) would have been visible only around sunset and not through the night. Still, such conjunctions are rare, so we are left with an almost supernatural feeling if the conjunctions really did happen around the time of Jesus’ birth. What are the odds of such rare events happening at the same time as the birth of someone who is arguably one of the most famous and important people in history?

However, it has also been suggested that the so-called star was actually a comet. Halley’s comet was visible around that time frame (12 BC) as was another bright object noted by Chinese and Korean astronomers (around 5 BC). While of unknown origin, the object seen by the Chinese and Koreans was apparently observed for over two months and did not appear to move. Such an object might have not been a comet but could have been a nova (a sudden brightening of a white dwarf star due to accretion processes that effectively cause an explosion and an increase in brightness that lasts days to weeks). While a comet or nova is a possible explanation for the Christmas Star, historians do not believe a cometary origin is likely. Comets were seen as bad omens back then, and certainly no one would associate the birth of Jesus with a bad omen.

An alternate explanation for the Christmas Star is that it was not a nova but rather a supernova, an explosion that indicates the death of a massive star. In this stage, a star will be extremely luminous as it expels most of its material. The remnant of such an event is either a neutron star or a black hole. Since supernovae are very bright and can be visible for several weeks or even months, it is probable that such an event would be noted by anyone observing the sky at the time of Jesus’ birth. However, it is difficult for astronomers in the present-day to say whether or not a supernova took place at that time, and there appears to be no records of such an event (which most certainly would have been noticed by someone, considering that supernovae are so bright that they can even be seen during the day when the sun is out!).

There is also the possibility that the Christmas Star was simply an ordinary star. But, astronomers can determine how the night sky appeared at the time of Jesus’ birth, and there is no obvious bright star that would be considered as a guide for the wise men. However, a part of the problem with understanding the origin of the Christmas Star is that the exact year of Jesus’ birth is not known. Based on various records, it is now believed to be between 7 BC and 2 BC, but there is some uncertainty there as even today different sources give different ranges of years for his birth. That said, something like Halley’s Comet, which appeared earlier in 12 BC, still seems an unlikely candidate for the Christmas Star.

Of course, some think the star may simply be a fictional aspect of the story of the birth of Jesus. This is because there are many facts that don’t add up. For instance, since Jerusalem and Bethlehem are just 10 km apart, a star would not be needed to guide the wise men in their travels. It is also likely that Jesus was not born in Bethlehem, but rather in Nazareth or elsewhere. The location of his birth would affect what star (if any) the wise men followed in their travels. Finally, we cannot rule out the possibility that the Christmas Star was of a supernatural origin, and truly occurred to signify the birth of a king. Furthermore, in some stories, the star was actually an angel. Needless to say, there is quite a bit of controversy in deciphering the nativity story. At this point, historians and astronomers have done pretty much all they can to solve this mystery. We may never know the true origin of the Christmas Star, but don’t let that stop you from celebrating Christmas (if you do that). To everyone else, happy holidays!